Conclusions
Tropical fungal diversity is surprisingly high and poorly understood. In our study, we found that the equivalent to a teaspoon of Amazonian soil can contain as many as 1 800 OTUs, which up to 400 were classified as fungi. It might therefore not be an exaggeration to call fungal diversity the ‘dark matter’ of life on Earth, alongside many other poorly studied groups. Our results highlight the importance of habitat type for fungal community composition. We also show that the known general patterns found for macro-organisms in Amazonia may not apply to fungi. It is important to improve our understanding of the patterns and drivers of fungal diversity and community composition since this is one of the most diverse eukaryotic kingdoms, whose members play key roles in nutrient cycling and biotic interactions in terrestrial ecosystems. Deforestation of Amazonia is increasing rapidly83, and to protect this forest it is fundamental to understand the processes underpinning ecosystem stability. For this, we have to focus on the distribution and diversity of organisms essential for the ecosystem functionality, including fungi.